1. Field of the Invention
The present invention relates to a thin-film magnetic head comprising a read magnetic head device of a CPP structure for reading the magnetic field intensity of a magnetic recording medium or the like as signals and a write-only induction type magnetic conversion device as well as a head gimbal assembly (magnetic head system) and a hard disk system (magnetic disk system), each incorporating that thin-film magnetic head.
2. Explanation of the Prior Art
(1) Thin-film magnetic heads are now required to have higher sensitivity and higher output to keep up with large capacities and size reductions of hard disk drives (HDDs). To meet such demands, improvements in the properties of thin-film magnetic heads are now under intensive development.
A thin-film magnetic head is ordinarily of a composite structure wherein an induction type recording device is stacked on a reproducing device using a magneto resistive effect device (MR device) in proximate relation. As well know in the art, the recording device is broken down into two types, i.e., a longitudinal recording device wherein the recording layer of a magnetic recording medium is longitudinally magnetized, and a perpendicular recording device wherein the recording layer is magnetized perpendicularly with respect to film plane. Most MR devices forming part of the reproducing device use a spin valve layer (hereinafter called the SV film). Still, thin-film magnetic heads using a ferromagnetic tunnel junction layer (hereinafter referred to as the TMR layer), too, have been vigorously developed and now put to practical stages, because of a possible resistance change rate that is at least twice as large as that of the thin-film magnetic head using the SV film.
The SV film and the TMR layer differ in the direction of conduction of sense currents and, hence, in head structure. In general, the head structure wherein sense currents conduct parallel to film plane is called a CIP (current-in-plane) structure, and the head structure wherein sense currents conduct perpendicularly to film plane is referred to as a CPP (current-perpendicular-to-plane) structure. With the CPP structure where a magnetic shield itself can be used as an electrode, there is not essentially any short circuit (poor insulation) between the magnetic shield and the device, which becomes a grave problem with making the lead gap of the CIP structure narrow. For this reason, the CPP structure works very favorably for high-density recording.
The TMR layer, basically because of having the CPP structure, possesses the advantage as mentioned above. The SV film, too, is seeing a switchover from the heavily used conventional CIP structure to the CPP structure to ensure the advantage of the CPP structure as mentioned above. For instance, multilayer structures of the specular or dual type are exemplified.
With the CPP structure, the first and second shield layers located with the MR device sandwiched between them also serve as electrodes for supplying sense currents. The first shield layer is located on a slider substrate. The slider substrate is constructed of Al2O3—TiC (hereinafter acronymed as AlTiC) improved in terms of wear resistance, and AlTiC is higher in electric conductivity than Al2O3 or the like. Accordingly, the first insulating layer is provided on an end face of the slider substrate, and the first shield layer is formed on the first insulating layer. Then, the second insulating layer is filled in between the first shield layer and the second shield layer, and the MR device is located within the second insulating layer.
On the second shield layer, there is provided the third insulating layer, on which a recording device is provided. The recording device has a coil, a magnetic circuit and a recording gap. The coil is insulated and supported by an organic or inorganic insulating layer. The magnetic circuit is to guide a magnetic flux generated by currents passing through the coil, comprising a magnetic layer (lower magnetic layer) that opposes the second shield layer via the third insulating layer and a magnetic layer (the second magnetic layer) that forms the magnetic circuit with the lower magnetic layer. The recording gap is provided somewhere in the magnetic circuit.
In the field of magnetic recording, by the way, higher write frequencies have been applied so as to keep pace with demands for higher data transfer rates, and recording devices and reproducing devices have been slimmed down so as to meet demands for higher recording densities. Thin-film magnetic heads now on use can follow current write frequencies, and device shape can match well with high-density recording on demand as well.
However, demands for higher data transfer rates and higher-density recording know no bounds; sooner or later, they will not be met for the following reasons.
A prior art CPP type thin-film magnetic head has a typical structure in which the first insulating layer is interposed between the slider substrate having electric conductivity and the first shield layer, the second insulating layer is filled in between the first shield layer and the second shield layer, the third insulating layer is interposed between the second shield layer and a recording device-forming magnetic layer (lower magnetic layer), and the coil of the recording device is insulated and supported by an organic or inorganic insulating layer. Consequently, such a parasitic capacity as set forth below is equivalently yielded in the thin-film magnetic head.
First, between the coil of the recording device and magnetic layer (lower magnetic layer), the first parasitic capacity C1 occurs with the coil-supporting organic or inorganic insulating layer as a capacity layer, and between the magnetic layer (lower magnetic layer) and the second shield layer, the second parasitic capacity C2 occurs with the third insulating layer as a capacity layer. Further between the second shield layer and the first shield layer, the third parasitic capacity C3 occurs with the second insulating layer as a capacity layer, and furthermore between the first shield layer and the slider substrate, the fourth parasitic capacity C4 occurs with the first insulating layer as a capacity layer.
With the above parasitic capacity circuit, as high-frequency write currents are passed through the coil, it causes the first C1, the second C2, the third C3 and the fourth parasitic capacity C4 to charge by the high-frequency write currents.
In the CPP type thin-film magnetic head, the second shield layer for generating the second parasitic capacity C2 and the first shield layer for generating the fourth parasitic capacity C4 are each positioned on both sides of the MR device or they differ in position, and the third parasitic capacity C3 is generated between the second shield layer and the first shield layer.
For this reason, the terminal voltage V2 of the second parasitic capacity C2 as viewed at the second shield layer is different from the terminal voltage V4 of the fourth parasitic capacity C4 as viewed at the first shield layer, and the ensuing differential voltage (V2˜V4) appears between the first shield layer and the second shield layer. In association with a voltage applied to the coil for conduction of write currents, this differential voltage (V2˜V4) oscillates, appearing between the first shield layer and the second shield layer in a crosstalk form. The crosstalk caused by the voltage applied to the coil for conduction of write currents incurs reproducing device deterioration. In addition, the higher the write frequency, the sharper the change in the writing voltage becomes and, hence, the higher the crosstalk voltage becomes. Thus, as the frequency of the write current becomes high, the detrimental effect of crosstalk grows large, resulting in further deterioration in the properties of the reproducing device.
Especially with a magnetic head using a reproducing device having a reduced section so as to keep up with higher-density recording, that detrimental effect grows large. When it comes to the SV film, this offers some problems such as reduced service life due to acceleration of electromigration, and deterioration in the magnetic properties due to acceleration of intermetallic diffusion. When it comes to the TMR device, on the other hand, the insulating layer present between ferromagnetic layers is likely to break down.
Moreover, a mutual difference between the second parasitic capacity C2 as viewed at the second shield layer and the fourth parasitic capacity C4 as viewed at the first shield layer renders extraneous noises likely to enter the magnetic head from the slider substrate side, giving rise to errors.
(2) As already described, the thin-film magnetic head is now required to have more improved performance to keep pace with an improvement in the plane recording density of a hard disk system. For the thin-film magnetic head, a composite type thin-film magnetic head is widely used, having a structure wherein a reproducing head having a read-only read magnetic head device and a recording head having a write-only induction type magnetic conversion device are stacked together on a substrate.
The read magnetic head is generally broken down into two types depending on in what direction a current (sense current) for the detection of a magnetic field is conducted with respect to the stacked device structure.
That is, it is broadly divided into a device of the CIP (current-in-plane) type wherein a current is conducted along the multilayer plane of the stacked device structure and a device of the CPP (current-perpendicular-to-plane) type wherein a current is conducted in the stacking (perpendicular) direction of the stacked device structure.
The former device is exemplified by a CIP type giant magneto resistive (GMR) device, and the latter by a CPP type GMR device or a tunnel magneto resistive (TMR) effect device.
In particular, a magnetic head equipped with the latter CPP type read magnetic head device has usually a structure wherein the upper and lower surfaces are sandwiched between a lower shield layer and an upper shield layer. Usually, the lower shield layer and the upper shield layer also serve as electrodes, and a sense current is applied between the lower and the upper shield layer in such a way as to allow the current to conduct in the stacking (perpendicular) direction of the device.
Generally, the thin-film magnetic head has a structure wherein the read magnetic head device and write magnetic head device are formed on the slider substrate. For instance, the slider substrate is formed of AlTiC (Al2O3—TiC), and an underlay film typically formed of Al2O3 is formed on the substrate for the purpose of making insulation between the AlTiC and the magnetic head device.
In the thin-film magnetic head, by the way, there are Joule heat from the coil layer in the induction type magnetic conversion device and heat in association with eddy current losses from the upper and lower magnetic layers. These heats end up with the so-called TPTP (thermal pole tip protrusion) phenomenon in which the overcoat layer covering the entire device is thermally expanded to force the magnetic head toward the surface of the opposing magnetic disk.
To hold back such a TPTP phenomenon, for instance, to radiate the above coil heat and coil eddy current loss heat to Al2O3—TiC, it is effective to reduce the thickness of the underlay film. However, the inventors have found that the thickness reduction of the underlay film leads to a phenomenon in which noises entering the slider substrate from outside grow more at the lower shield layer (also serving as an electrode) close to the slider substrate. Further, the inventors have noticed that such noises are amplified by a preamplifier, bringing about an undesired result with the noises superimposed on output signals.
In some cases, a heat generator is intentionally provided to make active use of the TPTP. However, the propagation of heat to the magneto resistive effect layer (device) must be limited as much as possible to maintain the ability to read signals.